Pressure-responsive instrument of the bourdon spring type



Sept. 25, 1928. 1,685,457

D. c. LAMB PRESSURE RESPONSIVE INSTRUMENT OF THE BOURDON SPRING TYPEFiled June 9, 1927 INVENTOR: W ,a' M

A; ATTORNEY.

Patented Sept. 25, 1928.

UNITED STATES PATENT OFF DONALD C. LAMB, OF ROCHESTER, NEW YORK,ASSIGNOR TO 1,685,457 ICE.

TAYLOR INSTRUMENT COMPANIES, OF ROCHESTER, NEW YORK, A CORPORATION OFNEW YORK.

PRESSURE -RESPONSIVE INSTRUMENT Application filed June 9,

This invention relates to pressure-responsive instruments of the Bourdonspring type.

ne object of the invention is an instrument of the class referred to,which is accura tely responsive to all changes of pressures within therange for which it is designed.

Another object is to roduce a reliable 'instrument re uiring a reatively small bulb.

Another 0 ject is an instrument practically :0 insensitive to theeffects of temperature changes.

The principal and more general object is the provision of an instrumentof the character involved, having certain desirable characteristics andbeing better suited for particular purposes than instruments heretoforeprovided.

For a full understanding of the invention, its distinctive features'bothas to construc- ZO tion and operation and its advantages, reference ismade to the accompanying drawings,

wherein Fig. l is a front elevation, partly in section of a structureembodying the invention;

Fig. 2 is an end view thereof, a part being removed, and

ig. 3 is a view similar to Fig. l of another embodiment of theinvention. V

In the drawings 10 is a multiple-convolu- 80 tion spring of the Bourdontube type con nected at its inner end to a support 11 which defines aconduit 12 for fluid connection with acapillary,

or free end of the spring is closed up in the usual way to make it fluidtight against relatively high pressures. v p

The structures thus far described, repre-' sents a usual and generallyknown device.

he invention in its broadest and most essential aspect consists of astrip 13 disposed in the tube, being secured thereto at its inner orstationary end, and extending preferably to the free end. A

The significance of the strip 13 is this: For heat-dynamic reasons, itis practically necessary to reduce the volume of the spring to aminimum. In the first instance a large volume of fluid in the springwould in some cases cause changes of pressure due to temperature changesor would materially increase the error caused thereby. Secondly, a largevolume in the spring would require a correspondingly large bulb.

Now, while tubes may be rolled down substantially flat leavingpractically \no space as is Well understood. The outer practice thesensitivity tending to niove the spring tube or THE BOURBON srnmo'rirru.

1927. Serial No. 197,644.

spring of desirable mechanical characteristics, it Was necessary toselect tubes of heavy stock and relatively thick walls, which in turnrequire a high fluid ressure for operation and involve serious unctionaldisadvantages for that reason.-

I have found that it is possible to produce a pressure-responsiveinstrument of desirable mechanicalcharacteristics susceptible tooperation at relatively low pressure and respon sive to relatively smallchanges in pressure, by making the ourdon spring of relatively thinstock provided the tube stock is not rolled down flat but is left inWhat may be called a slightly oval condition in cross-section. Theincrease in volume caused the eby is neutralizedby the filler strip 13.T5

The strip 13 thus is primarily a filler compensating for the increase ofspace incident to the changes in the Bourdon tube. In practice, however,I do not propose to use a filler 0t hap-hazard properties i. e. for thesole purpose of filling an excess space, irrespective of itscharacteristics in other respects. I propose to use a filler strip ofahigh degree of resiliency adapted to mechana compound action. areavailable for making a suitable filler strip 3, I preferably use highgrade steel.

strip is inserted in the tube and coiled together with the tube. WVhenthe tu as part of a gas or liquid-filled tube systetn is exposedpractically constant for 10h limits of the expan-' chosen and determinedto closing position. This co-operation of the filler spring 13 with thespring tube 10 is highly beneficial to the operation of the latter. Thefunction of the spring tube and all tubes of th e Bourdon type, is toassume a position no which is a function of the pressure within it.While the tubes are made of resilient material, they are not highlysensitive as springs and at least cannot compare as springs with springsnot in the form of tubes. They have, in particular the disadvantage thatat lower pressures their position is not sufliciently definite to beaccurate. A filler spring 13 thus artificially adds that degree of trueresiliency which the spring tube 13 alone is inherently lacking. Themechanical effect is much the same as though the resiliency of thespring tube proper were increased.

In one practical and what I consider at present as the preferredembodiment of the invention I propose to include as at least a part of aresilient filler strip 13, a thermostatic strip 13, so disposed that anincrease of temperature tends to cause a contraction of the spring tubeand a decrease of temperture permits an increase in the expansivemovement of the tube. I have found that for temperature compensation athermostatic strip extending only a fraction of the length of the tubeis sufficient and the remaining part to the free end of the tube may beany suitable spring united with the thermostatic strip as by Welding orbrazing or the like.

In practice, the dimensions of the thorniostatic strip are determined tosuit the conditions involved and then there is joined to it a Strip ofsteel, brass or other suit-able material to make the required length.The composite stri is then inserted in the tube to be used orming thepressure-responsive element. The tube is then coiled to the requiredshape. In Fig. 3, I have shown the thermostatic strip 13 as a bimetallicstrip of usual construction.

There is considerable latitude in the construction of the strip 13, butfor the reasons above pointed out, I preferably use such material ormaterials as to best satisfy all requirements for a good instrument.

lVhile a tube such as described is more generally applicable, it isparticularly useful in connection with gas-filled systems.

I claim:

1. In apparatus of the character described, the combination of apressure-responsive tube and a liller core therein consisting of a stripof resilient metal substantially filling the space defined by the wallsof the tube, a portion of the strip consisting of thermostatic material.

52. In apparatus of the character described, the combination of apressure-responsivctube and a filler core therein consisting of aresilient thermostatic strip and a. resilient metal strip joined theretoand extending to the free end of the tube.

3. In apparatus of the character described, a Bourdon tube of resilientmeta-l having substantially parallel opposing ,W'AllS in close proximityto each other, a core of resilient metal substantially filling the spacedefined by the Walls and asupport for the tube rigidly connected to thelatter, the said core being rigidly connected with the tube at the pointof connection of the latter with the support and being tube at itsopposite end.

In testimony whereof I affix my signature.

DONALD C. LAMB.

free to move relatively to the 7 0

